Hydrocephalus
Definition Expansion of the ventricular system due to increased intraventricular pressure, mostly due to abnormalities in the resportion, production, or flow of CSF. Confirmatory tests for normal pressure hydrocephalus *CSF withdrawal trial *History: classic clinical triad with gate apraxia, dementia, and urinary incontinence *Indium labeled CSF study with ventricular reflux, no flow over convexities at 24 to 48 hours **Indium is instilled into the CSF space through a lumbar puncture procedure **normally the tracer is reabsorbed over the convexities without ventricular reflux in a short amount of time (2 to 24 hours) **if there is communicating hydrocephalus and normal pressure hydrocephalus there will be a be flux of the tracer into the ventricles with lack of tracer accumulation over the convexities 24 to 48 hours after instillation *Marked aqueductal flow void *Trial of ventricular shunting (acid test) *Trial of lumbar drainage (72 hours) Components *Spaces **Lateral Ventricle **3rd ventricle **Cerebral aqueduct **4th ventricle: the last ventricle to dilate in hydrocephalus due to its anatomic proximity to the posterior fossa structures **Foramen of Luschka and Magendie *Structures **Arachnoid villi: sensitive structures readily damaged by insults. As protein levels in the CSF increase, the arachnoid villi become more susceptible to decreased absorptive capacity. Causes #Overproduction of CSF: Now questionable, first thought to be due to choroid plexus carcinoma or papillomas, but may be causing underabsorption of CSF as highlighted below. However, lateral ventricle choroid plexus papilloma may be a real cause of hydrocephalus. #Underabsorption of CSF at the arachnoid villi level due to blockage ##tumoral hemorrhage adhesions ##high protein levels ##intraventricular debris ##If a choroid plexus papilloma happens in the 4th ventricle then the foramina of Luschka and Magendie may be blocked. ##pathology at arachnoid granulation/villi ##infectious meningitis ##ventriculitis ##ependymitis ##subarachnoid hemorrhage ##carcinomatous meningitis ##noninfectious inflammatory meningitis (sarcoidosis) ##chemical meningitis (fat, arachnoiditis, intrathecal medications) ##mucopolysaccharidosis ##obstruction at the skull base ##Chiari malformations ##achondroplasia ##dandy walker cysts ##arachnoid cysts at foramen magnum ##Blockage of the flow of CSF ##Obstruction of Lateral Ventricles ###Colloid Cyst: A type of communicating hydrocephauls, classic for blocking the foramina of Monroe. Located in the anterior region of the third ventricle. Pre-contrast CT shows high density. MR shows high intensity on T1 and T2. Signal is variable however depending on the cysts composition. #Tumors #Choroid plexus papilloma #Ependymoma #Meningioma #Neurocytoma #Subependymal giant cell astrocytoma ##Obstruction of Third Ventricle ###Aqueductal webs, fenestrations, diaphragms ###Congenital aqueductal stenosis (Autosomal recessive) ###Tumors ####Craniopharyngiomas ####Ependymomas ####Hypothalamic gliomas ####Pineal neoplasms ####Vein of Galen aneurysms ##Obstruction of Fourth Ventricle ###Tumors ####Astrocytomas ####Choroid Plexus Papilloma ####Ependymoma ####Medulloblastoma (PNET) ##Congenital Aqueductal Stenosis: The cerebral aqueduct is the most narrow portion of the CSF outflow tract and therefore most prone to obstruction. An X-linked recessive disorder. Target group is children. Presents clinincally with enlarged head cirumference and radiographically with dilated and enlarged lateral and third ventricles, however the fourth ventricle is normal since it is distal the obstructing lesion. ##Aqueductal webs, septa or diaphragm: May block the cerebral aqueduct. ##Neurofibromatosis type 1: May block the cerebral aqueduct. ##Inflammatory and neoplastic disorders can block the cerebral aqueduct. ##CRASH syndrome (Corpus callosum hypoplasia, Retardation, Adducted thumbs, Spastic paraparesis, Hydrocephalus): X-linked disorder ##Obstruction at any Site ###Arachnoid cysts ###Complications of hemorrhage, infection, synechiae ###Cysticercosis ###Hematomas: especially posterior fossa strokes ###Meningiomas ##Trapped ventricles ###4th ventricle: Aqueduct of Luschka, Magendie, and Sylvius are occluded. Differential Diagnosis Differ in prognosis and therapy Hydrocephalus Atrophy Radiology Diagnostic Strategies The most sensitive indicator of hydrocephalus will be enlargement of the temporal horns or anterior recesses of the third ventricle. Sagittal MRI: to distinguish extrinsic compression versus aqueduct anomaly. CSF flow imaging: Use to diagnose aqueductal stenosis. Normal CSF signal should be bright; however, dark signal is seen on a flow scan if there is restricted flow like in aqueductal stenosis. Phase-contrast MR: With velocity encoding set to 10-15 mL/sec to assess aqueduct flow. FLAIR: Interstitial edema will be present in periventricular zone. due to transependymal CSF migration into adjacent white matter Pitfalls There may be normal high-intensity at angles of the ventricle in middle-aged patients which represent ependymitis granulosa. *Dilation of chiasmatic, infundibular, suprapineal recesses of the third ventricle *Rounding of the frontal horns *Effacement of sulci *Enlargement of ventricles out of proportion to sulcal dilation *Periventricular smooth high signal representing transependymal CSF exudation (best seen on FLAIR) *Accentuation of the aqueductal signal void *Narrowing of mamillopontine distances *Papilledema *Corpus callosum compression against the falx if the hydrocephalus is long standing *If aqueductal stensosis **Abnormal signal in the corpus callosum body **Scalloping of dorsal surface of corpus callosum **Tethering of pericallosal vessels Types Obstructive Hydrocephalus Noncommunicating *Due to physical obstruction along the CSF space (CSF outflow levels). Can use a shunt for therapy. Communicating *Due to abnormalities in absorption at the level of the arachnoid villi or incisura of the foramen magnum. Needs brain surgery for correction. Normal Pressure Hydrocephalus/Adult Hydrocephalus *Classical triad of gait apraxia, urinary incontinence, and dementia. *Patients have enlarged ventricles from communicating hydrocephalus with particular enlargement of the temporal horns. *May show evidence of transependymal CSF leakage on MRI or CT. *MRI shows accentuation of cerebral aqueduct flow void. External Hydrocephalus *Maybe due to immaturity of the arachnoid villi with a decreased ability to absorb CSF *usually seen in children younger than age 2 with a rapidly enlarging head circumference *neurologically these children are normal *CT or MRI will show dilation of the CSF spaces over the frontal lobes and a long interhemispheric fissure, however there will be relatively normal sized ventriclesprobably related to how the cranial sutures are still open Therapy *Ventricular shunts **most accurate predictors of a good response to shunting are: ***absence of central atrophy or ischemia ***gait apraxia as the dominant clinical symptom ***upward bowing of the corpus callosum with flattened gyri and ballooned third ventricular recesses ***prominent CSF flow void ***no history of intracranial infection or bleeding (non-idiopathic normal pressure hydrocephalus) ***a positive indium tracer study *Subarachnoid shunts *Third ventriculostomy *Surgical correction of offending lesion